The present invention relates, generally, to digital phase difference detecting circuits and, more particularly, to a digital phase difference detecting circuit which detects a phase difference between an input signal and a reference signal at high speed.
A phase difference between an input signal and a reference signal is obtained in various kinds of signal processing. An analog or digital circuit which detects phase difference generally has a multiplier. However, the linearity of the phase difference output of such a phase comparing circuit is poor; the phase difference output becomes distorted in the form of a sinusoidal curve. An analog phase comparing circuit is easily affected changes in the ambient temperature and the lapse of time, and it is difficult to manufacture as an integrated circuit. Such problems do not occur in a digital phase comparing circuit.
However, with a digital phase comparing circuit, when the input signal includes an amplitude modulated signal component, the amplitude modulated signal component appears in its phase difference output. Hence, in this case, there is a serious disadvantage in that it is impossible to detect a phase difference between the input signal and the reference signal accurately.